The pharmaceutical industry is involved in the discovery and development of medicines that improve our health. Drug discovery and development requires vast sums of money and inordinate amounts of time. Specifically, current methods used to identify and validate “targets” and to optimize drug structures in the pharmaceutical industry are particularly difficult and inefficient in large measure due to deficiencies in analytical techniques. An appropriately chosen detection technology and the instrumentation required to perform the detection are vital to the success of any assay. This is particularly true for high throughput screening, which requires continually higher throughput, lower costs, and higher sensitivities for lower quantities of reagents.
A variety of analytical techniques are used to characterize interactions between molecules, particularly in the context of assays directed to the detection and interaction between biomolecules and of biomolecules with small chemical entities. For example, antibody antigen interactions are of fundamental importance in many fields, including biology, immunology and pharmacology. In this connection, many analytical techniques involve binding of a “receptor” such as an antibody to a support, and contacting the bound receptor with an “analyte” such as an antigen. After contact between the receptor and analyte, one or more characteristics are measured which are indicative of the interaction, such as the ability of the receptor to bind the analyte.
There are numerous methods of studying protein protein interactions, including fluorescence, surface plasma resonance, mass spectrometry, and chemiluminescence. The goal of these studies is to determine what the protein of interest interacts with and how specific are the interactions. The data from these assays provides information on how proteins function in biological systems.
In the important and economically significant field of Medical Diagnostics, a variety of assay types are performed for many analytes of many different (chemical) types. The analytes are typically substances that indicate the health or disease status of a human or animal subject. Also, analytes that indicate the status of therapy are of great interest. There is a broad, unmet need in this field for general methods to measure accurately and reliably ligand-receptor interactions. Presently, most methods currently used in the diagnostics industry use employ labels such as a fluor. There is an increasing need however for measurements of many analytes in a single specimen. Moreover, the activities of the Human Genome Project and the burgeoning field of proteomics are identifying many new analytes and there is a pressing need for methods by which valid new assays can be developed quickly.
Surface Plasmon Resonance (SPR) is a “label free” method of assay development and is promising due to the possibility that it is faster to develop for any specific application and more reliable than label requiring methods such as those based on fluorescence. SPR systems and methods are known. Generally speaking, SPR is observed as a change such as a dip or reduction in intensity of light reflected at a specific angle from the interface between an optically transparent material and a thin metal film, and depends on among other factors the optical path length, i.e., the integral product of refractive index and physical thickness, of the medium and the quantity and distribution of such refractive material close to the metal surface. A change of refractive properties at the metal surface, such as by the adsorption or binding of material with different optical properties (typically index of refraction) than the medium in which the SPR metal surface is immersed, causes a corresponding shift in the angle at which maximum SPR occurs and which can be related quantitatively to the quantity of material that binds or adsorbs. To couple the light to the interface with the assay such that SPR arises, alternative arrangements are used; either a metallized diffraction grating (Wood's effect), or a metallized glass prism or a prism in optical contact with a metallized glass substrate (Kretschmann effect).
While SPR is a promising technology, there are concerns associated with SPR that inhibit its wide spread use. One problem is that conventional methods for SPR lead to less sensitive results than fluorescence results. Another problem is that SPR has not been capable of high-throughput in terms of assays/unit time. Yet another limiting factor is non-specific binding to the sensing surface, a problem common to all types of direct-measuring sensors, i.e. where no labelled reagent, such as an enzyme or a fluorophore, is used to provide the detected signal. Since SPR generates a signal for all material bound to the surface having an index of refraction different than the surrounding ambient medium (solution), the analyte cannot be distinguished from non-specific material.